The connections in a small dynamoelectric machine are typified by the lengths of bare copper wires which join the stator coils in electric motors. Insulation of those small connections is usually accomplished by application of micaceous insulating tape after the connections are made from a few strands of wire and fastened together, for example, by brazing. Because in many cases, the actual connection is only several inches long, has an irregular geometry and is located in a crowded part of the machine, the insulation normally has to be applied manually, a very slow and laborious process.
In larger machines, such as hydroelectric or steam turbine generators, connections are often made using large copper tubes or bars. These connecting parts may be taped and impregnated prior to installation. In any case, however, because of the irregular shapes involved, much or all the work must be done by hand.
A technique of applying such insulation, without the need for taping, would be of great benefit in the manufacture of dynamoelectric equipment. In addition to the obvious savings in labor and time, the cost of materials would be substantially reduced because insulating tape production involving mica paper fabrication, lamination, etc., would be avoided. Also, less expensive wet ground mica would be used instead of the fluid-split or calcined mica required for tape manufacture.
Heretofore electrodeposition of mica has been a recognized means of providing an electrical insulation coating or covering. Thus, Shibayama et al., U.S. Pat. No. 4,058,444 discloses such a process for providing insulation for coils of rotary machines, mica and a water dispersion varnish being used in a coating bath formulation. Other patents describe the electrophoretic deposition of mica through the use of water dispersion resins in similar manner to bind the deposited mica particles. Japanese patent issued to Mitsubishi Electric Corp. (Japanese Patents Nos. 77 126,438, 81 05,868 and 81 05,867) are directed along this same line, but none of them discloses the in situ electrodeposition of mica on electrical connections.
German Pat. No. 1.018,088 issued to H. W. Rotter describes the use of electrodeposited mica for insulating electrical connections, and sets forth a coating bath formulation which contains extremely finely-divided mica (&lt;1 micron). In addition, the possibility of using a silicone resin emulsion to aid in binding the flakes of mica together is mentioned.
Other applications of electrodeposited mica appear in the patent literature which involve the use of a binder either in the form of a water dispersion polymer or an aqueous emulsion. Objects to be coated such as wires, plates, and perforated plates are mentioned.
None of these prior art procedures has proven to be satisfactory enough to displace the manual technique with all of its drawbacks. For one reason, the coating compositions are unable to withstand prevailing conditions of the manufacturing environment, coalescing or coagulating when agitated or allowed to stand for prolonged periods. Additionally, the emulsions and dispersions used heretofore result in coatings which are not of uniform thickness, particularly on irregularly-shaped conductor substrates because the different levels of electrical field strengths cause corresponding variations in insulating coating thickness.
The generally-recognized, long-standing demand for answers to these problems, having not been met through any of the concepts disclosed in the foregoing patents or elsewhere in the patent art, has persisted to the present time.